Emission controls for internal combustion engines have become increasingly important as concern over environmental damage and pollution have been increasing, prompting legislators to pass more stringent emission controls. Much progress has been made in improving exhaust emission controls. However, crankcase emission controls have been largely neglected.
Crankcase emissions result from gas escaping past piston rings of an internal combustion engine and entering the crankcase due to high pressure in the cylinders during compression and combustion. As the blow-by gas passes through the crankcase and out the breather, it becomes contaminated with oil mist. In addition to the oil moist, crankcase emissions also contain wear particles and air/fuel emissions. Only a small number of heavy diesel engines have crankcase emission controls. The majority of current production diesel engines discharge these crankcase emissions to the atmosphere through a draft tube or similar breather vent contributing to air pollution. Some of the crankcase emissions are drawn into the engine intake system causing internal engine contamination and loss of efficiency.
The released oily crankcase emissions coat engine sites, such as the inside of engine compartments or chambers, fouling expensive components and increasing costs, such as clean-up, maintenance and repair costs. As the oily residue builds up on critical engine components, such as radiator cores, turbocharger blades, intercoolers and air filters, it becomes a "magnet" for dust, grit and other airborne contaminants. Particulates in the contaminated oily crankcase emissions include particles and aerosols. The accumulation of the particulates on these components reduces efficiency, performance and reliability of the engine.
In addition to increasing engine performance and decreasing maintenance intervals and site/critical engine component contamination, crankcase emission controls are becoming increasingly important in reducing air pollution. Engine emissions include both crankcase and exhaust emissions. Because of reductions in exhaust emissions, the percentage of the total engine emissions due to crankcase emissions has risen. Therefore, reducing crankcase emissions provides a greater environmental impact with engines having low exhaust emissions.
Furthermore, most of the crankcase particulate emissions (CPE) are soluble hydrocarbons, as opposed to the exhaust emissions which are mainly insoluble organics. The crankcase particulate emissions are oil related, with ethylene (C.sub.2 H.sub.4) being predominant. Therefore, separating the oil and returning the cleaned oil free crankcase emissions to the engine inlet for combustion increases engine efficiency.
Crankcase flow and particulate emissions increase dramatically with engine life and operating time. Thus, the environmental impact and engine efficiency from recycling the crankcase emissions increase with operating time. For example, in buses having diesel engines, the crankcase particulate emissions represent as much as 50% of the total exhaust particulate emissions.
Crankcase emission control systems filter the crankcase particulate emissions and separate the oil mist from the crankcase fumes. The separated oil is collected for periodic disposal or return to the crankcase.
Crankcase emission control systems may be "open" or "closed" systems. In open crankcase emission control systems, the cleaned gases are vented to the atmosphere. Such open systems are manufactured by Diesel Research, the assignee of the present application. Other open systems are "Emission Absorber/Ecovent" manufactured by Nelson Industries, "Oildex" manufactured in California, and "Condensator" manufactured in Colorado. Although open systems have been acceptable in many markets, they pollute the air by venting emission to the atmosphere and suffer from low efficiency. Closed systems eliminate crankcase emissions to the atmosphere, meet strict environmental regulations, and eliminate site and external critical component contamination.
In closed crankcase emission control systems, the cleaned gases are returned to the engine combustion inlet. "Airsep" by Walker Engineering is one such closed crankcase emission control system. Another closed system by Walker Engineering uses a canister type filter and a vacuum limiter. Other closed systems by Diesel Research include a two-component system which has a crankcase pressure regulator and a separate filter. In addition, "Oildex" and "Condensator" have also been used in closed systems.
Closed crankcase emission control systems require a high efficiency filter and crankcase pressure regulator. The high efficiency filter is required to filter out small sized particles to prevent contamination of turbochargers, aftercooler, and internal engine components. The pressure regulator maintains acceptable levels of crankcase pressure over a wide range of crankcase gas flow and inlet restrictions.
In a closed system, the crankcase breather is connected to the inlet of the closed crankcase emission control system. The outlet of the closed crankcase emission control system is connected to the engine air inlet, where the filtered blow-by gas is recycled through the combustion process.
FIG. 1a shows a prior art closed crankcase emission control system 100 disclosed in the U.S. Pat. No. 4,724,807 to Walker. The closed crankcase emission control system 100 comprises a vacuum limiter 110 and an in-line oil separator 120 that has a circular centrifugal pattern. A hose 125 interconnects the vacuum limiter 110, the separator 120, and a crankcase breather 130 which is located on a valve cover 135. The vacuum limiter 110 limits the crankcase and engine intake vacuum. This is achieved by venting the crankcase emissions to the atmosphere or pulling ambient air into the hose 125 through an air tube 145 connected to an air filter (not shown) that fits over the entire vacuum limiter 110. The venting to the atmosphere by the vacuum limiter 110, through the air tube 145 transforms the closed system 100 into an open system.
The separator 120 receives crankcase emissions from the hose 125 and clean air from a silencer filter 150. The separator 120 relies on a centrifugal pattern to separate oil from the crankcase emissions. The output from the separator 120 are cleaned crankcase emissions, which are provided to the combustion inlet of the engine, through the induction system or the turbo air intake 155 for turbo-charged engines. The exhaust manifold 160 and the turbocharger 162 (FIG 1a), for turbo-charged engines, are coupled to an exhaust 165. The separated oil drains back to the engine block 140 or the oil pan 170 through a drain hose 175 connected to the separator 120. A check valve 180, shown in FIG. 1b, is connected between the separator 120 and the oil pan 170. The check valve 180 allows oil to drain from the separator 120 and the oil pan 170 but prevents oil or gas flow in the opposite direction.
FIG. 1b is a block diagram representation of FIG. 1a. In FIG. 1b, as well as the remaining figures, identical elements are identically numbered. FIG. 1b shows the separator 120 connected to the turbo air intake 155 of a turbocharger system 190. The turbocharger system 190 includes a compressor 192, a turbocharger 194 and an aftercooler 196.
FIG. 2 shows the separator 120 in greater detail. The separator 120 has an annular housing 210 containing first, second and third baffles 220, 230, 240. The third baffle defines a channel 250. One end of the channel 250 is a primary gas inlet 260 connected to the silencer filter 150 for receiving ambient air. The other end of the channel 250 is a gas outlet 270. A secondary gas inlet 280 receives oil contaminated crankcase emissions from the crankcase breather 130, through the hose 125. The separator 120 separate oil from the crankcase emissions and outputs the cleaned crankcase emissions and the air from its primary gas inlet 260 through the gas outlet 270.
The separated oil drains through a drain coupling 290 which is connected to the engine block 140 or to the oil pan 170 through the check valve 180 and the drain hose 175 (FIGS. 1a-b).
FIG. 3 is a cross-section of the separator 120 showing its the centrifugal pattern, wherein the flow of crankcase emissions are shown by arrows 310. As shown in FIG. 3, baffles 220, 230, 240 are arranged so that there is no straight line flow path between the secondary inlet 280 and the outlet 270. As the oil contaminated crankcase emissions flow through the separator 120, the oil impacts and condenses or is adsorbed on the surfaces of the baffles 220, 230, 240. The cleaned crankcase emissions enter the channel 250 through an opening 310 of the third baffle 240. The cleaned air then exits the channel 250 through the outlet 270 and enters the intake air turbo 155, which then transports the air as usual.
FIG. 4 shows a block diagram of another closed crankcase emission control system 400 comprising a filter/separator 410, a control valve 415 which regulates pressure in the crankcase. The filter/separator 410 incorporates the check valve 180, shown in FIG 1b, to form an integral check valve 420 attached to an oil drain outlet 425. Furthermore, unlike the separator 120 of the system 100 shown in FIG 1b, the filter/separator 410 is connected off-line. The filter/separator 410 has a foam filter 430 which filters the oily crankcase emission and separates the oil which is collected in an oil reservoir 440 located below the foam filter 430.
Such a crankcase emission control system 400 is manufactured by Diesel Research, the assignee of the present application and distributed by Parker Hannifin Corporation, Racor Division.
Several problems exist with current systems including low efficiency. For example, the oil separator 120 suffers from efficiency of less than 20%. This low efficiency has caused internal engine contaminations. Furthermore, the system 100 shown in FIG. 1b, is not an effective closed system. The vacuum limiting vacuum limiter 110 used in the closed system 100 either introduces outside air (requiring filtration) or bypass crankcase emissions to the atmosphere under high vacuum conditions effectively becoming an open system.
Another problem is finding room to locate the separate components of the prior art crankcase emission systems, such as the vacuum limiter 110, the control valve 415 and the separator/filter 120, 410 shown in FIGS. 1a and 4.
Compact packaging, while maintaining high efficiency, is a major consideration in crankcase emission control systems. Attempts have been made to reduce packaging size requirement by making an integral separator/air filter in a single unit such as the separator/filter 120, 410. However, separate components, i.e., the vacuum limiter 110, the control valve 415, and the separator/filter 120, 410, are used for pressure control and filtration. Having separate filtration and pressure control components not only present problems associated with packaging, i.e., finding space on the engine to locate them, but also result in higher cost of system parts and labor.
Existing inertial separators used in closed system, such as the system 100 shown in FIG. 1a, are of low efficiency, and barrier filters are of medium efficiency. Barrier filters, such as the coalescing filter 430 (FIG. 4), which are capable of filtering small particles, require a high pressure drop for proper filtration and clog quickly, thus requiring frequent replacement.
The determination of efficiency of the filter used in a closed system include the buildup of oil film in the aftercooler and the resultant deterioration in engine performance leading to premature engine overhaul. As oil film deposits in the aftercooler, the heat transfer rate from the compressed high temperature air to the water coolant decreases. As the air temperature to the engine proper increases, the full power capability of the engine decreases. Fuel efficiency reduction, control system and fuel injector fouling result from low efficiency filters.
A single flapper type valve, which opens to the atmosphere, not only requires a fresh air filter, with its associated loading effects, but also admits substantial diluted air to the emissions. This transforms a closed system into an open system and makes control through the necessary wide range of conditions difficult.
Thus, it is an object of the present invention to provide a closed crankcase emission control systems that is compact and combines various components into a single integrated unit, yet is efficient, simple and inexpensive to manufacture. It is another object of the present invention to provide a pressure control assembly that performs three functions, namely, regulating pressure, separating oil and agglomerating particles. It is a further object of the present invention to reduce the interval between changing filters, yet providing for efficient filtration. It is yet another object of the present invention to use the pressure drop across a pressure control mechanism to aid filtration combined with agglomeration and separation.